Methyl isobutyl ketone (MIBK) is a colorless organic compound with the formula (CH3)2CHCH2C(O)CH3, which is widely used as an industrial solvent for nitrocellulose, lacquers, and certain polymers and resins. Another major use is as a precursor to N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylene diamine (6PPD), an antiozonant used in tires.
Methods for producing MIBK are well known in the prior art. One such method involves manufacturing of MIBK from acetone via a three-step process (Kudo, S. “Formation of Higher Molecular Weight Ketones from Acetone or Isopropanol,” J. Chem. Soc. Japan Ind. Chem. Sec., 58 (1955), 785-787). Firstly, acetone undergoes a liquid phase aldol condensation reaction at low temperature in the presence of a basic catalyst to give diacetone alcohol (DAA). DAA is then dehydrated to give mesityl oxide (MO) with an acid catalyst at atmospheric pressure. Finally, MO is dehydrogenated to give MIBK. The three-step process is disadvantageous because of high initial investment, the need for cooling equipment for acetone condensation to DAA, and acid contamination due to the use of a homogeneous acid catalyst.
More recently, one-step processes combining the three steps into one have also been disclosed. U.S. Pat. No. 3,953,517 (assigned to Veba-Chemie Aktiengesellschaft, Germany) describes a method for producing MIBK by contacting acetone and hydrogen in the presence of a cation exchange catalyst containing a noble metal, at a temperature of about 50-200° C. and a pressure between 60 and 100 atmospheres. U.S. Pat. No. 5,149,881 (assigned to Mitsubishi Kasei Corporation, Japan) describes a similar method with palladium and a metal oxide and/or metal hydroxide treated with an organosilicon compound as the catalyst. U.S. Pat. No. 5,684,207 (assigned to Industrial Technology Research Institute, Taiwan) describes a one-step process including reacting acetone and hydrogen in the vapor/liquid phase at a temperature of about 100-300° C. and a pressure of about 100 to 1000 psig, in the presence of a modified ZSM-5 catalyst. Most commercial one-step MIBK processes these days employ a palladium-doped cation exchange resin, such as the Sasol process exclusively licensed by Uhde GmbH, Germany (Uhde GmbH, “Uhde Technology Profile: MIBK” (2005)). The major drawback of such one-step processes is the need for operation at an elevated pressure to keep the hydrogen in the liquid phase. Furthermore, the multifunctional catalyst that can effect condensation, dehydration, and hydrogenation reactions is typically expensive, and numerous byproducts may form as a result of combining the three chemical transformation steps in one reactor.
The use of two different catalysts for the production of MIBK from acetone has also been suggested. U.S. Pat. No. 6,762,328 (Catalytic Distillation Technologies, Pasadena, Tex.) (“the '328 patent”) discloses a process which involves two reaction zones. The first zone is a catalytic distillation zone where acetone is reacted over an acidic ion exchange resin catalyst to form a product stream containing MO, water, and optionally, DAA, other by-products, and unreacted acetone. A product stream containing MO and water is recovered from this mixture, and separated into two liquid phases in a decanter. The MO rich organic stream is sent to the second reaction zone where it is reacted with hydrogen to form MIBK in the presence of a hydrogenation catalyst such as Ni on Al, Pd on Al, or Pd on C catalyst.
This process also suffers from disadvantages. When the product stream from the first reaction zone includes DAA, other by-products, and unreacted acetone, such components are removed by distillation. This involves distilling acetone twice, and MO and water once, which are both energy intensive. In another embodiment described in the '328 patent, the first reaction zone is operated so that substantially all of the acetone is converted, and the product stream contains at most traces of acetone. To achieve such a high acetone conversion, the process requires high catalyst loading in the first reaction zone, which is disadvantageous from the catalyst cost point of view.
Moreover, the process disclosed by the '328 patent uses a catalytic distillation column operating at total reflux as the first reaction zone, operating at a temperature of 100-120° C. in the catalyst bed, a temperature of 120-150° C. in the column reboiler, and a pressure of 2-7 bar. A continuous energy supply is needed in the reboiler to keep the reaction mixture in a state of boiling. Moreover, it is known that higher temperatures, such as those used in the '328 patent, promote the formation of heavier condensation products.
It is desirable to have a process which operates at as mild conditions as possible. Moreover, in order to minimize the energy cost for operating the process, it is desirable to have a separation sequence in which evaporation of the desired product or recycled component is minimized. Further developments are needed.